1. Field of the Invention
This invention relates to centrifugal pumps used in industrial applications to process slurries, and specifically relates to centrifugal pumps having a volute especially configured to process highly abrasive slurries.
2. Description of Related Art
Centrifugal pumps of the volute type are well-known in the art and have a pump casing that is generally circular or toroidal in shape. The outer peripheral region of the circular pump casing defines the volute region of the pump. The volute region surrounds an impeller positioned within the pump casing and is positioned to receive fluids which are processed by the impeller. The inner volute region of the pump casing thus serves as a collector of fluid being forced outwardly by the impeller under centrifugal forces.
Typically, the volute region of the pump casing changes in volume as it extends about the circumference of the pump casing. That is, the axial cross section of the volute region of the pump casing taken at any point around the circumference of the pump casing reveals that the volute has a volume that changes. The varying volume of the volute about the circumference of the pump casing effects the flow dynamics of the pump as the fluid moves from the cutwater region of the pump casing to the discharge nozzle.
Additionally, the type of fluids being processed by the pump further dictate the selected volume or shape of the volute. It is well known that regions of instability occur in centrifugal pumps of the volute type. Such flow instabilities can cause fluctuations in fluid pressure and can adversely affect pump efficiencies. Instabilities in the flow are also known to be caused by the type of fluids being pumped (i.e., clear water versus slurries).
U.S. Pat. No. 5,127,800 to Hyll, et al., describes how volute pump design differs between a pump used to process clear water (i.e., fluid that is low in, or essentially devoid of, solids content) and a pump used to process slurries. Namely, the impeller of a clear water pump has shrouds the thickness of which is typically comparatively smaller because the fluid, being devoid of particulates, does not cause wear on the impeller. However, the shrouds of the impeller in a slurry pump are described as being thicker to compensate for degradation of the impeller due the solids content of the fluid. The increased thickness of the impeller shrouds results in the development of turbulent flow patterns as the fluid exits the impeller and enters the volute region of the pump. The patent to Hyll, et al., therefore discloses a volute that is particularly shaped to compensate for the turbulent flow patterns that result in slurry pumps.
The volute design that is disclosed in the '800 patent to Hyll et al., is selectively configured with arcuate contours the shape or radius of curvature of which varies about the circumference of the pump casing. Specifically, the volute contour at the cutwater region of the pump, when viewed in axial cross section, comprises a single symmetrical curvature. The contour of the volute gradually changes to comprise a trio of connected concave areas the radii of curvature of which change along the circumference of the pump casing in the direction of the discharge nozzle. The cross section configuration of the volute at any point along the circumference of the pump casing in the '800 patent is essentially symmetrical about a plane radially bisecting the volute region.
The volute design disclosed in the '800 patent to Hyll, et al., is particularly suited for processing slurries of lower solids content at high flow rates. It has been found, however, that while the design of that volute provides stable performance curves, the design is prone to wear by abrasive solid particles in the pumped slurry. This is particularly true in slurry applications that are considered “heavy duty” by virtue of the size and coarseness of the solids contained in the slurry, such as crushed ore slurries.
When pumping heavy duty slurries, the impeller of the pump must be configured with aggressive expelling vanes on the front shroud of the impeller (i.e., the shroud adjacent the pump inlet) to protect the seal face from abrasive solids. More aggressive expelling vanes operate to create extensive outward oriented vortices behind the expelling vanes which keep abrasive solid particles in suspension in the volute of the pump and prevent the particles from infiltrating the seal area. The vortices created by aggressive expelling vanes transfer additional velocity to the abrasive solid particles, however, which wears out the convex portions of the contoured volute design disclosed in the '800 patent and degrades the wall surface of the volute.
Thus, it would be beneficial in the art to provide a configured volute for a centrifugal pump that is designed to address the volute degradation encountered in the processing of slurries, particularly those containing coarse and/or more abrasive solids particulates, while still providing stable performance curves.